LM2585SX-ADJ/NOPB National Semiconductor, LM2585SX-ADJ/NOPB Datasheet - Page 22

IC MULTI CONFIG ADJ 3A TO-263-5

LM2585SX-ADJ/NOPB

Manufacturer Part Number
LM2585SX-ADJ/NOPB
Description
IC MULTI CONFIG ADJ 3A TO-263-5
Manufacturer
National Semiconductor
Series
SIMPLE SWITCHER®r
Type
Step-Up (Boost), Flyback, Forward Converterr
Datasheet

Specifications of LM2585SX-ADJ/NOPB

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
Adjustable
Current - Output
3A
Frequency - Switching
100kHz
Voltage - Input
4 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (5 leads + tab)
Primary Input Voltage
40V
No. Of Outputs
1
Output Voltage
12.6V
Output Current
3A
No. Of Pins
5
Operating Temperature Range
-40°C To +125°C
Filter Terminals
SMD
Input Voltage Primary Max
40V
Rohs Compliant
Yes
For Use With
551011367-061 - BOARD WEBENCH LM2577,LM2585/87
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Other names
*LM2585SX-ADJ
*LM2585SX-ADJ/NOPB
LM2585SX-ADJ
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Application Hints
PROGRAMMING OUTPUT VOLTAGE
(SELECTING R
Referring to the adjustable regulator in
voltage is programmed by the resistors R
lowing formula:
Resistors R
can be compared with the 1.23V internal reference. With R
between 1k and 5k, R
For best temperature coefficient and stability with time, use
1% metal film resistors.
SHORT CIRCUIT CONDITION
Due to the inherent nature of boost regulators, when the out-
put is shorted (see
V
R
OUT
1
= R
= V
2
1
(V
and R
REF
OUT
1
AND R
(1 + R
/V
2
Figure
divide the output voltage down so that it
REF
1
is:
1
2
− 1)
/R
)
38), current flows directly from the
2
)
where V
where V
Figure
1
and R
REF
REF
38, the output
= 1.23V
= 1.23V
FIGURE 39. Flyback Regulator
FIGURE 38. Boost Regulator
2
by the fol-
2
22
input, through the inductor and the diode, to the output, by-
passing the switch. The current limit of the switch does not
limit the output current for the entire circuit. To protect the load
and prevent damage to the switch, the current must be ex-
ternally limited, either by the input supply or at the output with
an external current limit circuit. The external limit should be
set to the maximum switch current of the device, which is 3A.
In a flyback regulator application
dard transformers, the LM2585 will survive a short circuit to
the main output. When the output voltage drops to 80% of its
nominal value, the frequency will drop to 25 kHz. With a lower
frequency, off times are larger. With the longer off times, the
transformer can release all of its stored energy before the
switch turns back on. Hence, the switch turns on initially with
zero current at its collector. In this condition, the switch current
limit will limit the peak current, saving the device.
1251556
(Figure
1251555
39), using the stan-

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